Which of the following statements is false? a. two or more atoms combine chemically to form a molecule. b. two or more different substances combine physically to form a mixture. c. two or more different atoms combine chemically to form an element. d. two or more elements combine chemically to form a compound.

Air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. air enters the heat exchanger at 95 kpa and 20°c at a rate of 0.6 m^3/s. the combustion gases (cp = 1.10 kj/kg°c) enter at 160°c at a rate of 0.95 kg/s and leave at 95°c. determine the rate of heat transfer to the air and its outlet temperature.